Analysis of the cellular DNA content was carried out in 162 children with ALL and 34 children with AML admitted to the university children's hospital Münster between 1979 and 1984. DNA aneuploidies were identified at a similar frequency in ALL (40%) and AML (44%). However, the degree of DNA aneuploidies (DNA-index) was significantly lower in aneuploid AML (median 1.09) than in aneuploid ALL (median 1.19). We found a significantly lower incidence of DNA-aneuploidies in T-ALL (3/21; 14%) as compared to non-T/non-B-ALL (60/137; 44%). No differences were found between children with and without DNA aneuploidy in PAS score and TdT activity. In non-T/non-B-ALL DNA aneuploidy is highly correlated with a long pretherapeutic history, with a low WBC and blast count and with a low serum LDH. Under the conditions of the ALL protocols BFM-79/81 and 81/83 no difference in the remission rate was found between the two patient groups. However, more relapses occurred so far within the group of children without DNS aneuploidy.